This invention relates generally to an electrode assembly for attachment to body tissue to sense electrical heart activity. The electrode is particularly suited for insertion through the vaginal passageway of a woman in labor and for remote controlled attachment to the fetus. The electrode provides heart signals to electronic monitoring equipment which displays an electrocardiogram and/or the heart rate.
A variety of remote controlled insertion tools and electrodes have been proposed for use in the body. For example, MacLean U.S. Pat. No. 2,839,049 describes a guide tube for insertion in the vaginal canal. The guide tube contains a wire having a handle attached to one end and a brush attached to the other end. Rotation of the handle causes rotation of the brush inside the womb.
H. D. Junge discloses an electrode for attachment to a fetus in a paper entitled "Eine Neue Technik Der Elektronischen Daueruberwachung Von Fetaler Herzfrequenz Und Wehentatigkeit Unter Der Geburt" published in Geburtshilfe Und Frauenheilkunde, Feb. 1969, pages 129-133. The electrode assembly includes a retaining coil mounted on a holder. The holder is coupled to a drive rod through releasable cooperating engaging means including prongs on the rod which engage depressions on the holder. The drive rod is disposed in a guide sleeve and the assembly is inserted into the vaginal canal until the retaining coil contacts the fetus. Thereafter, the external end of the rod is rotated, thereby to rotate the retaining coil and screw it into the fetus. The guide sleeve and drive rod are then removed from the vaginal canal and a signal lead extending from the retaining coil is attached to electronic heart monitoring apparatus.
Following the publication by H. D. Junge, others developed remote controlled electrode assemblies which screw retaining coils into body tissue. Ruttgers U.S. Pat. No. 3,750,650 discloses a fetal monitoring electrode assembly including a spiral electrode extending from a holder. A drive tube retains the holder by cooperating engaging means including slots in the drive tube and projections on the holder. In use the assembly is rotated to screw the spiral electrode into an unborn fetus. The guide tube and drive tube are then telescoped to release the electrode from the tubes and the two tubes are withdrawn from the vaginal canal.
Rasor U.S. Pat. No. 3,835,864 describes a remote controlled device for screwing a retaining coil into body tissue. The coil holder is rotated by a flexible drive rod inside a guide tube. The drive rod is coupled to the coil holder through cooperating engaging means which operates to release the coil holder from the drive rod after the coil is attached to the body tissue.
Hon, et al., U.S. Pat. No. Re. 28,990 also discloses a remote controlled device for screwing a retaining coil electrode into body tissue (a fetus) wherein the coil is rotated by a drive tube inside a guide tube. The drive tube is coupled to the coil by cooperating engaging means in the form of fins on the coil holder and slots in the drive tube.
One disadvantage inherent in electrode assemblies of the type described above is that they are characterized by complex insertion tool arrangements. Numerous components including guiding and driving tubes and releasable cooperating engaging means are required to achieve remote controlled rotation to screw the electrode coil into body tissue. These complex configurations are costly to manufacture and are often difficult to satisfactorily manipulate in use.
Another disadvantage of heretofore known electrode assemblies relates to the manner in which the electrode coil is applied to the body tissue. The retaining coil itself is usually small and formed with a few turns of sharply pointed stainless steel wire. When the coil is manually rotated by the insertion tool mechanism, it can easily be screwed deeply into body tissue. There is a danger that the electrode may be manually overdriven with consequent tearing of the tissue. In the case where the electrode coil is a few millimeters in diameter and applied through the vaginal canal to a fetus, the large torque transmitted by the insertion tool may drive the coil so deeply and tightly into the fetus that a plug of flesh is pulled out. Such coring by the electrode coil is traumatic to the fetus and precludes satisfactory electrode attachment for sensing heart activity.